Questions about the 8-head figure drawing method.

I feel as if I may be missing something important with the 8-head method in figure drawing, and would enjoy a little clarification if anyone can help. I understand that basically it is supposed to give you the size of your figure in respect to other figures within the piece as well as the figure in relation to it's surroundings. My confusion is how is this applied when the figure is either in motion, shown at an angle, or, in the case of comic books, in an extreme pose or action? Is this method only to give yourself an idea of the characters size in the designing stage of the character and then thrown out once you get into the actual creation of a piece, or is it merely to learn to compose the human form and once you do so you should be able to begin to eyeball it at any angle? This is something that has perplexed me for a long while, so, any help or direction to look for this answer would be greatly appreciated.
This is a character sketch for a comic I am working on for reference. I believe I am getting the hang of it, but, again, any help is greatly appreciated.

I would sketch it in different angles first and see what "feels" right. Use your 8 head high character as a guide for putting your character into other poses. I like freehanding (eyeballing) things in the beginning because the result can be so much more natural than starting with grids, or guides, etc....

I think you nailed the dilemma that I had while I was studying anatomy for the first time. I was diligently learning all those muscles and bones, expecting that all that knowledge would magically endow me with the ability to draw accurate figures. And then, as soon as the figure was not standing straight like a medical specimen, I had no idea what shapes those muscle and bones would take or even where they would be... I think there should be much more clarity in books and courses about the fact that all anatomy knowledge in the world will not help you with drawing a figure in movement or in non-schematic positions - not directly at least. The only thing that helps with that is drawing figures from models - a LARGE number of those. Knowing anatomy and proportions does help with drawing from life (or photos) and to make the brain absorb the knowledge from practice drawings a bit faster, I think.